1. Field of the Invention
The present invention relates to a method and apparatus for processing an eye fundus image, and in particular relates to a method and apparatus for processing an eye fundus image to display an eye fundus image in a manner that allows an eye fundus to be enlarged and stereoscopically observed.
2. Description of the Prior Art
A demand has traditionally existed for viewing an eye fundus in a stereoscopic shape for use in eye fundus examinations. Methods for stereoscopically viewing an optic cup of an eye fundus or the like have been proposed wherein an eye fundus camera having a two-aperture photographic stop provided with left-right parallax is used to capture an image of an eye fundus with each of the photographic stop and the captured images are then aligned side-by-side, displayed on a monitor and observed using a stereoscope.
In such instances, the relative positions of the two eye fundus images for stereoscopic viewing are aligned for display on a monitor (see Japanese Patent No. 2844458), or photographing conditional information such as the photographed left and right eye is recorded and stored along with the photographed image (see Japanese Laid-open Patent Application No. 2002-17681).
The eye fundus is stored in a memory as an electronic image. The eye fundus image stored in the memory is enlarged or scaled down in accordance with a user-specified magnification ratio, and displayed on a monitor as a visible image, so that the eye fundus image is observed after having accordingly been scaled up or down (Japanese Laid-open Patent Application No. 1999-28189).
However, a problem arises in that the angle of view of the images captured by the fundus camera is wide (45° or 20°), thereby making the depression optic cup insufficiently visible. Images are preferably captured at an angle of view of about 10° in order to respond to such a requirement. For this reason the additional introduction of high-magnification photography lenses having an angle of view of 10° is being considered for fundus cameras. Methods for newly providing high-magnification lenses as an attachment are theoretically possible. However, problems are presented in that the cost of the apparatus increases, and photographic proficiency becomes necessary because the fixation of a patient must be skillfully directed in order for a prescribed position to be photographed. Further problems are encountered because high-magnification photography inevitably results in a large amount of light being emitted on the eye fundus during the photographic process, making the method unrealistic.
To resolve the foregoing problems, the eye fundus can be photographed using electronic imagery, the magnification ratio of the image can be increased by image processing rather than via an optical process, and so-called digital magnification may be performed, as disclosed in Japanese Laid-open Patent Application No. 1999-28189. However, in order to change the magnification after the capturing of eye fundus images of a pair consisting of a left image and a right image, a magnification-changing procedure must be performed on each image. In addition, the size of the monitor cannot be changed, leading to the problem that stereoscopic viewing cannot be performed if the center of the image to be enlarged and displayed is not set at the same location in the left and right images.
Therefore, it is an object of the invention to provide a method and apparatus for processing an eye fundus image being capable of stereoscopically observing an eye fundus with a magnification adjusted to a desired ratio with a simple configuration.